This invention relates to acoustic waveguide electroacoustical transducing systems.
For background, reference is made to Bose U.S. Pat. No. 4,628,528 and Bose U.S. Pat. No. 6,278,789 B1, both of which are incorporated by reference herein.
It is an important object of the invention to provide an improved acoustic waveguide and electroacoustical transducing system which has a long waveguide channel within a relatively compact structure.
In an aspect, the invention features an acoustic waveguide for transmitting pressure wave energy produced by an electroacoustical transducer in a medium that propagates pressure wave energy. The acoustic waveguide has a tube defining a spiral-shaped channel with a length of L. The tube has a first end and a second end with a transducer opening for accommodating an electroacoustical transducer located adjacent to the first end of the tube. The second end of the tube is open the medium.
Embodiments may include one or more of the following features. The spiral-shaped channel may have a smoothly changing curvature with radius. Additionally, the inner walls of the waveguide may be contiguous. The effective length of channel L may be approximately one quarter of the wavelength of the lowest frequency pressure wave energy to be transmitted by the waveguide. The lowest frequency to be transmitted corresponds substantially to the frequency below which the output level commences falling substantially continuously with frequency. The tube may define a spiral shaped channel that has a rectangular cross section. The tube may define a spiral shaped channel that has a rectangular cross section. The tube may define a spiral shaped channel that is coiled in a single plane, forming a flat spiral, or coiled in a plurality of planes, forming a helical spiral.
In another aspect of the invention, an acoustic waveguide for transmitting pressure wave energy produced by an electroacoustical transducer in a medium that propagates pressure wave energy, the waveguide has a tube having a first end and a second end and formed in a spiral configuration. The first end of the tube is closed and the second end of the tube is open to the medium and a transducer opening for accommodating an electroacoustical transducer is located on the tube between the first end and second end of the tube. The tube defines a first spiral-shaped channel located between the transducer opening of the tube and the first end of the tube and a contiguous second spiral-shaped channel located between the transducer opening of the tube and the second end of the tube.
Embodiments may include one or more of the following features. The first spiral-shaped channel defined by the tube may have a length of ⅓L while the second spiral-shaped channel may have a length of ⅔L. The length of the first spiral-shaped channel, ⅓L, plus the length of the second spiral-shaped channel, ⅔L, plus end effect may be approximately equal one quarter of the wavelength of the lowest frequency pressure wave energy to be transmitted by the waveguide. The first and second spiral-shaped channels may each have a smoothly changing curvature with radius. The inner walls of the tube may be contiguous. The first spiral-shaped channel may have substantially the same cross-section as the second spiral-shaped channel. The cross section of the first and second spiral-shaped channels may be rectangular. The tube may be composed of PVC. The tube defining the spiral-shaped channel may be coiled in a single plane, forming a flat spiral. The tube may be coiled in a plurality of planes, forming a helical spiral. A transducer housing may be attached to the tube and the tube may have a second transducer opening located between the tube and the transducer housing. The tube may be of two-piece construction which may be assembled with screws, bolts, clips, adhesive, glue and the like.
In another aspect of the invention, a system for transmitting pressure wave energy in a medium that propagates pressure wave energy in a medium, the system includes an electroacoustical transducer having a vibratile surface and a spiral waveguide.
Embodiments of the invention may have one or more of the following advantages.
A spiral waveguide permits a long waveguide channel within a relatively compact structure. A long waveguide channel improves the bass response of a loudspeaker system, while a compact structure can be particularly convenient in a loudspeaker system where physical space is limited, such as in an automobile or portable stereo. Additionally, a spiral waveguide does not have any abrupt 90 or 180 degree bends in the channel, which minimizes unwanted turbulence in the waveguide channel. A spiral waveguide can also be configured to have an open and a closed end with a transducer positioned at a specific distance between the open and closed end in order to reduce the first peak in frequency response of the acoustic energy transmitted by the waveguide.
Other features, objects and advantages will become apparent from the following detailed description when read in connection with the accompanying drawing in which: